Process for treating molybdenite concentrates



T. H. DONAHUE ET AL PROCESS FOR TREATING MOLYBDENITE CONCENTRATES Filed Oct. 1l, 1935 MOL YBDE/V/Tf CO/VCE/VTHTE Patented Oct. 26, 1937 PATENT OFFICE PROCESS FR TREATING MOLYBDENITE CONCENTRATES Thomas H. Donahue and John B. Cunningham,

Tucson, Ariz., assignors to Donahue and Cunningham, a co-partnership Application October 11, 1935, Serial No. 44,636

10 Claims.

This invention relates to the treatment of thev ores of molybdenum.

Molybdenum occurs in naturemost commonly in the form of ores containing the mineral molybdenite, MoS2. Such ores may be concentrated by flotation methods which are effective and economical and yield high. grade products. Under proper operation the concentrate will contain 90% to 95% of M052.

The largest use for molybdenum at present is in the preparation of alloy steel Which has many excellent'properties. The molybdenum usually is added either as ferro-molybdenum or as calcium molybdate. The molybdenite concentrate is entirely unsuited for addition to steel, since its sulphur content would have an extremely deleterious effect.

The sulphide ore of molybdenum is moreover quite generally associated with sulphides of iron and copper. In treating such ores by flotation the iron and copper sulphides Will enter the molybdenite concentrate unless special conditions are adhered to and a differential notation operation is conducted. A fairly good separationy of the molybdenum and copper canbe made, but only at the expense of losing an important amount of the molybdenum. Copper is considered a very detrimental impurity in any molybdenum product used for steel alloying and commercial custom places a maximum limit of 0.3% copper content in molybdenite concentrates.,

This invention provides a method for cheaply,-

economically and. conveniently treating molybdenite concentrates which contain copper, pro- `ducing molybdates suitablyV free of copper and sulphur, and also recovering the copper in a marketable form, which constitutes a valuable byproduct.A

By the process of this invention molybdenite concentrates can be successfully treated no matter how much copper is present.

% chalcopyrite, equivalent to about 20% copper. Such ability to treat copper bearing materials is one of the salient features `of the invention and one of its chief sources of economy, since it not only permits a greater recovery of molybdenite in the flotation operation, but the copper is recovered as a valuable by-product.

' there are various impurities other than sulphur and copper Which are. very deleterious. Phos-V phorus and aresnicrespecially are veryharmful.V

We have suc-- cessfully treated concentrates Which containedv In the manufacture of molybdenum steel alloy` (o1. zs-is') nated from the nal product or at the Worst reduced to scarcely detectable traces.

Numerous processes for converting molybdenite concentrates to calcium molybdate or ferromolybdenum are described in the technical litery ature. A process which is commonly employed comprises carefully roasting the ore or concentrate at a low temperature and With liberal access of air, whereby the molybdenum sulphide is converted to molybdenum oxide, according to the following equation:

to form calcium molybdate, according to theV equation: l cao-iMoogecaMool This is the finished product of this process. It will be observed that the only possibility Vforeliminating impurities by this process is by volatilization. Copper, iron, silica and most of the arsenic and phosphorus are non-volatile under the conditions of the Vroasting and enter the finished product. l v Y The chemical principles upon which the present inventionV functions Will now be described. The practical application of these principles will be explained by description of the various .steps in the process. It is understood that the invention is not limited to the exact procedure described, but the scope of the invention is defined in the claims.

VThe principal steps of the process are shown inV l 4.5,

the flow sheet of the accompanying drawing.

'Ihe rst step in the process consists in thoroughly roasting the molybdenite concentrate which, as'stated above, need not be freeof cope per. This may be done in any suitable roasting furnace, such as a muiile, or in a hand operated reverberatory or in a mechanical furnace such as the MacDougal or Herreschoif. The chemical reaction ordinarily Ystated as representing the roasting of molybdenite has already been given. We have found that thisreaction does not com- When the 'Y 7o equivalent tothe molybdenumY content of the pletely describe the conditions,v but that, instead, the'reaction proceeds in tvvov distinct stages, represented by the equations:

The second reaction is more difficult to effect,

Vparticularly if any sintering occurs.

We have observed Wide difference in behavior of molybdenite concentrates from different sources,

particularly With respect to they tendency to form molybdenum dioxide. Since Ythe presence of molybdenum Vdioxide in the roasted prod- Y uct introduces diiiculties in the subsequent steps of the process, Ythe roasting operation is 'controlledrso as to produce as fsmall an amount as possible. We have foundothat best results are obtained by a prolonged roast at low temperature c untilalmost all of the sulphur is eliminated, rel Ymovingfrom the furnace, cooling, grinding and y L Ythe method We preferably employ, is to return' y715 and with free access of air.

during-the first two hours andincreasetoGOO" C.` at the end of the third hour. It Vis notnecessary to roast outV all oi thelsulphur in order to prevent introduction of sulphur into'the nished product,

but any molybdenum sulplrud'avvhich` is f not roasted at least to thel dioxide Will not be re#Y covered in the subsequent operations. Sulphides of and copper'areoosimultaneo-usly roasted, being converted Vlargely to the corresponding molybdates, but partly tothe sulphates, as shown Vby. the equations typifying lthe behavior Yof pyrite- Y Copper exhibits a marked tendency to form the sulphate, Whereas iron tends largely to form the molybdate. So far as possible it isdesirable to decompose-the copper and iron sulphates .during the roasting operation in the interest of reducing the consumptionl of reagents Vin the subsequent Y .opera-tions. VSulphates which are not so decomposed do not exert Vanyr other unfavorable .effect than consumption of .reagent andare not especially harmful. in reducing the content of sulphates to 1.25% S03 calculated on the Weight of roasted material.

During theV roasting a volatilization of minor imn puritiesoccurs, but this effect is unimportant.

We found that molybdenite concentrates from some sources are peculiarly diilicult c to roast. Marked sintering occurs and the contentl of molybdenum dioxide is unusually high. This may be Vcorrected'in certain cases byroasting returning tothe furnace for a short roast, for example one-half `hour at 500 C. '.As an alternative and preferableV method We mix with the concentrates,v before roasting, some material which will assist, in the roast. Such an inert. material as nely ground silica Will have. some beneficial effect. Sulphides of iron and copper may be employed to advantage and these may usually be obtained merely by` changing the conditions ofthe flo-tationrcper'at'ion by which the molyb- 'd'enuniV Vis loriginally recovered. When copper or iron or' both are used to aid'the roasting itis advantageous to employl an amount chemically concentrate to forrnthe molybdates of said metals. The most' advantageous Vmethod, and

part of "the vreach residue which Vconsists' largely We preferably main-,- Vtain the temperature at approximately 500 C.

We have found little diflculty of silica and iron and copper oxides. This has the addedradvantage of subjecting they material to more than one treatment.

TheV second step in our process consists of leaching Vthe roasted product With a fairly strong solution in which Vthe active ingredient is `a caustic alkali, hereinafter exemplified by caustic soda. Spinceothe process is cyclic in nature, this solution is derived from a later step of a previous cycle of operations and contains Aother compounds than sodium hydroxide in solution. For the purpose ofr explanationronly the sodium hydroxide content will be considered at this point,V since it is the only material taking partrin the reactions. The molybdenum trioxide of the .roasted material is rapidly dissolved by the so-L dium hydroxide, forming sodium molybdate, Vaccording to the equation:

Ferrie oxide and copper oxide are unaffected'and remain insoluble. Ferrie sulphate and copper sulphate react ,Withpthe sodium hydroxide, forming the respective insoluble hydroxides and soluble sodium sulphate,`according to the equations:

Fe2(SO4)3+6NaOH=2Fe(OH 3-l-3Na2SO4 CuSO4+2NaOH==Cu(OH) 2+Na2SO4 The resulting sodium molybdate solution is ac- V` cordingly completely free of iron and copper, but

Will contain allV the sulphur trioxdein the roasted ore in the form of sodium sulphate. Iron and copper molybdates, formedrin the roasting,

are completely decomposed by the Ycaustic solutions according to the equations:

We have found that if thereris a deficiency of caustic'soda during the'leaching operationrthe For this reason We prefer to operateY our process under such controlled conditions Vthat there is always an Vexcess of caustic soda `present. `We preferably maintain this excess alkalinity vat a minimum of 1.0 gram NaOH per liter, as determined by titrating with standardized hydro-Y chloric acid, using phenol phthalein as the indicator. We have found that at this alkalinity no insoluble iron or copper molybdates are formed.

We haveY also found that in case the proportions f of the leach have been improperly adjusted and the solution becomes acidi with simultaneous precipitation of copperk and iron molybdates, the

situation maybe corrected by increasing the rsi alkalinity Vto the'preferred minimum' value, for

example, by adding caustic solution'.v When this isdone the insoluble molybdates are decomposed in accordance with thevreactions previously given. VAlkalinity corresponding to Vabout 0.5 gram and even less of NaOH per liter has been found to be suicient'tc preventrprecipitation of the insoluble Ymolybdates or to dissolve them 'if they have been formed.V 1 'jV As previously pointed out, vthe caustic soda solutionrhas littleY or no power tov dissolve anyr molybdenum dioxide yWhich may be present. One Y of the novel features of our invention is the provision of means "to recover the' molybdenum d1" 75 lons per. pound of M003. vConcentrates with oxide. When the content of molybdenum dioxide in the leached residue is low, We preferably introduce anadditional step into the leaching 'operation. This step consists of the addition of i a reagent which is capable of acting as an oxidizing agent in alkaline solution; We preferably employ a relatively strong solution of sodium hypochlorite which oxidizes the molybdenum dioxide to the trioxide, in which form it is readily soluble in the caustic solution. The sodium chloride which results from the sodium hypochlorite Y does'not introduce any detrimental impurity'into the leaching cycle. Other oxidizing agents may be employed, such as, for example, gaseousv chlorine. In extreme cases, Where the content of molybdenum dioxide is unusually high, and the expense of providing oxidizing reagents during the leach would be burdensome, we preferablyr conduct the leaching operation Without any such added oxidizing agent, and subject the residue from the leaching to a second roasting operation and a separate leach, in which the proportion of solution to solids is reduced to correspondwith the lowered content of molybdenum trioxide in such material. We have also found that the various methods for overcoming the difficulty Which is introduced by the tendency to form inolybdenum dioxide during the roast may be advantageously combined in certain cases. For example, part of the residue may be mixed with are more rapid and complete and filtrations are` also more rapid. The use of hot solutions is not, however, essential for obtaining satisfactory leaching. We have carried out the leaching operation at normal atmospheric temperatures and obtained the same results as at higher temperatures, except that a longer time Was required.

Although we preferably operate the process elevated temperature in all steps, we do not limit the scope of our invention to any particular temperature at which the leaching operation is to be conducted. The leaching operation is con` ducted in tanks of suitable size and provided with means for agitation, such as a propeller. The tanks may be made of Wood, which conserves the heat, or of iron, since the caustic solutions do not exert any corrosive action on iron.

As Will be discussed in connection with one of the subsequent steps of the process, the strength of the cycling solution may be varied within rather Wide limits. We have found that generally satisfactory results are obtained by v having the return caustic solution which goes to the leaching operation have a content of 20 grams free caustic soda per liter, as determined by titration with standardizedl hydrochloric acid, using phenol-phthalein indicatore A solution of this strength will dissolve 28 grams M003 per` liter While being reduced to the minimum of 1.0 gram NaOH per liter, providedA the sulphate l content of the roasted material is not more than about 1.2% .$03. This is equivalent to 0.243 pound of M003 per gallon Aof solution, or 4.32v galabout 5%- copper Will yield a roasted product with about 85% M003. With such material the dissolving capacity of. the leaching solution is about 0.286 pound of calcine per gallon. Stronger solutions may be used, but cause rapid deterioration of filter cloths and the strength of solution here specified is sufciently concentrated to give economical operations Without handling undue volumeS.

- W e have found that the reaction is` quite rapid,

and with the heated solutions which We preferably employ, a leaching time of one hour isr volumes of fresh Water. When the original mof lybdenite concentrate contains `over 3% copper and only a small amount of insoluble matter, such as silica, We khave found the-residue will analyze;

about 20% copper. This material is admirably adapted for sale to a copper smelter as it is free of sulphur and has a highiron content which is of value as flux. Any gold or silver in the original concentrate will also be saved in-this residue, but usually there is only a small amount. The filtered solution from the leach will contain not only the sodium molybdate, but the small intentional excess of free caustic soda and the sodiumvsulphate derived from the iron and copper sulphates produced in the roasting operation. Moist molybdenite concentrates contain small amounts of phosphorus, arsenic, and vanadium. There is Vprobably a certain minor volatilization of these impurities during roasting, particularly of the arsenic. The filtered leaching solution usually contains Ya small amount of phosphate or arsenate radical, or some of both. The leaching solution being at all times alkaline absorbs carbon dioxide from the atmosphere with formation of sodium carbonate which must also be considered as an impurity.

'I'he third step of the process consists in the removal of all these impurities from the filtered leaching solution except the free caustic soda and the sodium sulphate, by precipitating them as the respective salts of the alkaline earth metals calcium, strontium, or barium, exemplified hereinafter by the salts of calcium, according to the following equations:

.The reactions are rather slow and We preferably employ a considerable excess of calcium molybdate, assisting the reaction by agitation and heating. We find it convenient, to carry out the purification reaction in a tank especially reserved for this purpose. 'Ihis tank should be of such size as t0 contain the totalvolume of filtrate from one cycle of the leaching operation. The tank is preferably provided with a steam jacket which ,isv particularly useful in case the plant has been shut down for sufficient time t0 permit the solutions to cool 01T. Since itis this operation which removes the carbonates and since the carbonates are derived almost entirely'by absorption of carbon dioxide from the atmosphere this purification operation should be carried out immediately before the final precipitation: of the molybdenum andthe solution, after purification,

should'be immediately precipitated to avoid new contamination of the nal calcium molybdate by calcium carbonate. We preferablyremploy cal'- cium molybdate equivalent to roughly ten times the impurities to be precipitated and agitateY for one hour at a temperature near the boiling point. At the ccmpletion'of the operation the mixture is given ample'time to settleand theclear liquid decanted off and passed Ythrough a ilterpress'tfrv clarify it. VThe thickened'residue isY allowed to remain in the tank and is used for severalsuccessive purication operations untilrits content of calciumfmolybdate is practically consumed. It is then removed, filtered and Washed and discarded, or further treated for the recovery of its molybdenum and vanadiur'nrcontents.V The calcium salts are almost crystalline and granular and settle rapidly to a small bulk. A wide variety of reagents may be Vused inthe purification of the molybdate solution. 'For' instanceother com# pounds of calcium, barium, and strontium, such as the chlorides,hydroxides,` sulfates, etc., may be used. Also compounds of other metals such as magnesum, Zinc, manganese, iron,raluminum and Vcopper may be used, but these Compounds 'gen-Y erally must be used in large excess and give pre'- Y cipitates which are difcult to filter.

The iiltered solution will contain Yabout 5% Na2Mo`O4, a little excess caustic soda, and a small amount of lsodium sulphate. The next, i. e. fourth, step in the process is the precipita-tion of the molybdenum as calcium,rbarium, or strontium .molybdate preferably by boiling Vwith milk of lime, according to the equation:

This reaction is' surprisingly rapid, consideringA the very low solubilityV of ther solid phases. For'V efficient operation, i. e. substantial completion of the reaction inv a reasonable time (1 to 2 hours), the temperature of the reaction mixture must be at least about 95 C. At 85 C. thepreactionr proceeds'very slowly. At Y90 C. the reactionis substantial, but still quite slow. Y

When employing CaiOH); as the precpitantY the reaction reaches van equilibrium depending@ upon, the concentration of caustic'alkali.- VY'The proportion of the total quantity of molybdenum in solution, precipitated, will vary VfromV about at a caustic soda concen-'tration:ofv aboutV .60 grams per liter to anrapparentrmaximum of about 90%. The molybdenum not precipitated is not lost due to the cyclical use of ,the solution. When employing the caustic sodaV concentrationY of 20 grams perliter aboveyreferred to, inthe Y leaching step, the precipitationV willlproceed Vto hydroxide.

As previously stated the lteredfsolutien fromr the leachcontains a small amount of sodium sul` phate. `At the causticity'atwhich the precipitaf'l tion of rcalciurn'-rnolylzzda'te is carried out, nor

' tially CaMoO4. the process, and after washing isrdried in any eyd. y K

calcium sulphate is precipitated, the reactiony washes andv by periodic vremoval of solution. The

washes and removed solution are stripped of molybdenum before discarding in a subsequent Y st'epof` the process. Y VIn theV preferred form in which we V,practice our invention the precipitation with lime is carried out in two stages. In the first stage the'ltered leaching solution contained in a steam jacketed iron tank provided with an agitator, is treatedy with a mixture of YCaMoO; and YCa(OI-I)z resulting from the second stage of the preceding cycle, and which was left in the tank. This mixture contains only enough CafOHl'z to precipitate roughly half of the of the molybdate which will be precipitated in the two stages. 'I'he solution 'is heated Vand. agitated in contact with this material forI about 42 hoursand then allowed kto settle.

The/,clear liquor isV decanted Y 01T to a second tank exactly similar to thefirstV one and without filtering, any small amount of calcium molybdate remaining suspended being of lnoimportance.v The thickened calcium molybd'ate is then filtered-in a filter press and the filtrate Yadded to the main bulk of thedecanted solution in the other tank. In this first stage of the precipitation there is a considerable ex-v cess of Na2MoO4 which tends to consume all the g Ca(OH)2 and gives a precipitate which is essen- I'his is the finished product of suitable manner.VV We have consistently produced CaMoO4 containing i3-45% molybdenum, compared to a theoretical content ofv 48%.

In the second stage of theA precipitation the solution isY treated with an'amount of Ca(OH)z equivalent to 85%/ ofthe total Vmolybdate in the solution prior to the first stage. This gives a considerable excess of calciuml hydroxide which tends to carry the reactionV tothe maximum pos- Y sible point as rapidly as possible. We preferably agitate lthe solution and heat it for another two hours, then allow to settle. The clear solution is Ydecanted off and passed through a filter pressV to vremove any suspended CaMoOi, which would otherwise be lost and the filtratev is returned to the leaching cycle." The thickened mixture of CaMoO4 and Ca OH 2 is left in the tank andthe next batch of solution from the leach is Vrun in j on top of it to become the first stage in the precipitati'on. ated solutionVV will analyze, under the conditions of leaching, etc., previously describedn as the pre#-v ferred conditions, approximately as follows: l

A l Y Grams/liter Free NaOH V V ;y 20.0v Na2M0O4. I V ..V 8.0 Ca(OH)2 1 0.03

plus anV additionalVV andY variable content Volf Y Na2SO4.

residue from vthe leaching and alsothe calciumv molybdate; This tends-toyincreasethe volume vThe vresultingY filtered and regenerof the solution in the cycle. The tendency to increase is partly compensated by the Water which is contained in the leach residue and in the final calcium molybdate as they leave the process and also by the water lost by evaporation from the hot solutions. If these two tendencies were made to balance each other, for example, by limiting the volume of wash water, the volume could be kept constant. However, if this were done the sodium sulphate content would increase after each cycle and ultimately introduce diculties. We preferably control the volume of the cycling solution and at the same time the concentration of sodium sulphate by the following two expedients: `When washing the two filter cakes from the process onlyV the first and strongest washes are returned to the main volume of solution of the process. rlIhe final and weaker wash waters are treated in a special operation for recovery of the molybdenum 4content. Also after each cycle of operations we remove a small portion of the filtrate from the final precipitation of the calcium molybdate. This serves to control the building up of the sodium sulphate. We have found that of the volume of the solution is a practical proportion to remove.

The molybdenum is recovered from the coinbined weak washes and the portion of the main solution discarded, by precipitation with nely ground gypsum according to the following equation: NazMOOa-l-CaSOdI-Iao:

The reaction proceeds as indicated only when there is present an excess of caustic soda, which is, of course, present in large amount in the portion of the main solution removed. This excess caustic soda reacts with the gypsum to produce calcium hydroxide, according to the equation:

The reaction serves to completely precipitate the molybdenum and leave only sodium sulphate in solution.

1Ne preferably perform this operation in a small tank provided with an agitator. lWe have found it necessary to heat the mixture. The reaction is fairly slow and we preferably continue the agitation for about two hours, employing a slight excess only of gypsum. The mixture is then transferred to a lter and washed. The ltrate and washings are discarded since they contain only the sodium sulphate which it was desired to eliminate. The mixed precipitate of CaMoO4 and Ca(OI-I)2 is employed in the operation of precipitating the calcium molybdate in the main cycle of operations. Any unconsumed gypsum which it contains is converted to calcium molybdate and sodium sulphate in this operation. We are aware that various other reagents might be employed for this operation, such as the strong mineral acid salts of the alkaline earth and heavy metals, but we preferably employ gypsum because it is readily obtainable in high purity, is Very cheap and serves the double purpose of being a source of calcium and an acidic material which in effect neutralizes the caustic soda and permits the reaction to proceed to completion.

As a result of the removal of a portion of the main cycling solution, there is a loss of caustic soda from the process. It is necessary to make this up by addition of caustic soda to the process. If the proportion removed is 5% it will be necessary to add at each cycle an amount of caustic soda equivalent to 5% of the sodium content in the whole'volume of cycling liquid. In practice we have found the consumption of caustic soda to be equal to 0.025 NaCl-l per pound of CaMoO4 produced. This is only 50 pounds of NaOH per ton of -CaMoO4 and is not an important item of cost. The consumption of gypsum and hydrated lime isabout in excess of the theoretically calculated requirements based on the CaMoO4 produced and without correcting for impurities in the commercial qualities of the gypsum and hydrated lime. It will therefore be obvious that our process is extremely economical as regards consumption of reagents and the cost thereof.

The invention has been described with particular reference to the use of sodium hydroxide as the dissolving agent for the molybdenum oxid and theuse of calcium molybdate as the agent for Vpurifying the resulting solution and the use of lime orcalcium hydroxide as the precipitating agent for the molybdenum in solution. It is to be understood, however, that the other caustic alkalies, particularly caustic potash, may be used in place of caustic soda in the leaching step; that oxids, hydroxids, molybdates or other suitable salts of metals of the group consisting of Ca, Ba, Sr, Mg, Zn, Mn, Fe, Al, Cu, etc., may be used in the purification, and that the hydroxids of barium or strontium may be used in place of calcium hydroxid in the precipitating step.

We claim:

1. Process which comprises roasting a molybdenum sulphide containing material to the conversion of at least a part of the molybdenum sulphide content thereof to molybdenum trioxide, leaching the roasted material with asolution containing ycaustic alkali, separating the resulting solution containing alkali metal molybdate from undissolved residue, purifying the solution by agitating it in the presence of Yalkaline earth metal molybdate, separating the so purified solution from solid matter, reacting the purified solution with an hydroxide of an alkaline earth metal and recovering the so-precipitated alkaline earth metal molybdate from the resulting caustic alkalicontaining mother liquor.

2. Process which comprises leaching a material containing iron molybdate associated with impurities with a solution containing caustic alkali, separating the resulting solution containing alkali metal molybdate from undissolved re`sidue purifying the solution by agitating it in the presence of an alkaline earth metal molybdate, separating the so-purified solution from solid matter, reacting the purified solution with an hydroxid of an alkaline earth metal and recovering the soprecipitated alkaline earth metal molybdate from the resulting caustic alkali-containing mother liquor.

3. Process which comprises agitating a solution containing alkali metal molybdate, caustic alkali and impurities in the presence of an alkaline earth metal molybdate, separating the sopurified solution from solid matter, reacting the purified solution with an hydroxid of an alkaline earth metal and recovering the so-precipitated alkaline earth metal molybdate from the resulting caustic alkali-containing mother liquor.

4. Process of purifying a solution containing an alkali metal molybdate and one or more ipurities of the group consisting of alkali metal phosphate, vanadate, arsenate and carbonate, which comprises contacting said solution with a finely divided compound of the group consisting of the jalkallne earth Vmetal molybdates Vand soluble alkaline earth metal compound capable of reacting with alkali metal molybdates to the formation of alkaline earth., metal molybdatea: the latter inquantity insurlicient to convert the bulk I of the alkali metal molybdate content of the solution to alkaline earthV metal molybdate, separating the precipitated impurities from the solution 'and'reacting the purified solution with an hydroxid of an alkaline earth metal in quantity rsuilicient to precipitate the bulk of the molybdate content thereof asA alkaline earth metal molybdate.

5. Process which comprises leaching a material containing molybdenum oxide with a solutioncontaining alkali metal hydroxid, separating theV resulting solution containing alkali metal molybdate from undissolved residue, purifying the alkali metal molybdate'solution by agitating it VWith an alkaline earth metalmolybdate, sepa-Y ratingV the so-purined solution from solid matter,

k reacting the purified solution With alkaline earth metal hydroxid thereby precipitating the molybf Yderiurnco'ntent of the Ysolution as alkaline earth metal4 molybdate and regenerating the alkali metal content of the solution as alkali metal hydroxid, separating the alkaline earth metal molybdate from the solution containing regenerated alkali metal hydroxid and usingnsaid solution for leaching a fresh quantity of material n containing molybdenum oxide.

6. VIn the process of recovering a molybdatc from sulphide ores containing molybdenum, the steps which consist in roasting a concentrate thereof in the presence of sufficient added-metal compound of the group consisting ofthe sulphids and oxids of'iron and copper to convert the molybdenum content to a molybdate of said metal,

' and leaching the roasted'concentrate with a 'caustic alkali solution. Y

7. YProcess Vfor the precipitation of a molybdate Y from a solution containing an alkalimetalrnolybdate and freeY caustic alkali .Whichcom'prises Yiagitating the solution at a temperature of at least about 85 C.' with a mixture of calcium molybdate and calcium hydroxide, the latter in Yquantity insufficient to precipitate allA of the molybdenum contento'f the solution as calcium molybdate, separating the'resulting precipitate, agitating the separated solution at a temperature of at least about 85 C. with an excess of calcium hydroxide thereby producing a mixture ofV cal- Y cium molybdate andcalcium hydroxide, and using said mixture of calcium molybdate and calcium hydroxide in the treatment of a further quantity Vof solution containingV alkali metal molybdate.

.8. In the process for the recovery of a' molybdate from a solution containing-an alkali metal molybdate an alkali metal sulfate andY free caustic alkali the step Which comprises agitating the solution with calcium sulphate in quantity suflicient` Vresulting solution containing alkali metal molybdate from undissolved residue, purifying the molybdate solution by agitating theV same'with calcium molybdate, separating the so-puried Y solution from solid matter, reacting the puried solution, at a temperature of at least about 95 C. with a mixture of calcium molybdate and calcium hydroxide, the latter in quantity insufficient to Y precipitate all of the molybdenum cont-ent of the solution as calcium molybdate, separating the resulting precipitate, agitating the separated solution at a temperature of at least about 95 C. with an excess of calciumrvhydroxide thereby producing a mixture of calcium molybdate and kcalcium hydroxide, and using said mixture of calcium molybdate and `calcium hydroxide in the treatment of a further quantity of solution con- Ytaining alkali metal molybdate.

' l0. In the process of recovering a molybdate from ores containing molybdenum ther steps Which consist in leaching a material derived from the ore containing molybdenum trioxide and molybdenum dioxide with a solution containing caustic alkali in the presence of sodium hypo-. chlorite.-

THOMAS H. DONAHUE.

JOHN B. CUNNINGHAM. 

